Biosynthesis of estrogens can be carried out by means such that androgens are subjected to oxidation and elimination of formic acid by an enzyme called aromatase, and aromatized. Therefore, if the action of aromatase can effectively be inhibited, it is expected to be useful for treatment of diseases caused by estrogens, and in line with this expectation, several aromatase inhibitors have already been found to be effective for treatment of breast cancer and prostatic hypertrophy.
Aromatase inhibitors are also effective for treatment of other diseases caused by estrogens, for example uterine cancer, ovarian cancer, endometriosis, male gynecomastia, male e infertility related to oligospermia, etc.
As known steroid aromatase inhibitors, there have, for example, been known testolactone (Merck Index, 10th edition, 8999), 4-hydroxy-4-androstene-3,17-dione and its esters (U.S. Pat. No. 4,235,893), 1-alkylandrosta-1,4-diene-3,17-dione derivatives (Japanese Laid-Open Patent Publication No. 13796/1985), 4-substituted androstene-3,17-dione derivatives (Japanese Laid-Open Patent Publication No. 189295/1986), 6-methyleneandrosta-1,4-diene-3,17-dione derivatives (Japanese Laid-Open Patent Publication No. 12797/1987), 16-oxaandrosta-1,4-diene-3,17-dione (Journal of Medicinal Chemistry, 32, 651, (1989)), 7.alpha.-substituted thioandrostenedione derivatives (Journal of Medicinal Chemistry, 21, 1007, (1978)), etc.
However, these steroid aromatase inhibitors, when administered into living bodies, are liable to be inactivated through metabolism, and are still not satisfactory for clinical use.
The present inventors found that a series of steroid compounds wherein a hetero atom is introduced into the ring D part and the 7-position of the steroid skeleton is substituted with a specific substituent have a very excellent aromatase-inhibiting activity, and moreover, are slow to undergo inactivation through metabolism.